The present invention relates to the use of fly ash to make building materials including wallboard.
Fly ash that results from coal combustable products is a readily available commodity. Coal burning plants for generating electricity produce thousands of tons of fly ash. Disposal of the fly ash continues to be a major challenge. Because of its abundance and the difficultly in finding entities who want the fly ash, practical uses for the fly ash have been previously advanced for the purpose of expanding the market for fly ash Disclosures and proposals have been made for using fly ash as part of building materials including building blocks, panels, ceiling components, as well as building insulation.
Notwithstanding the efforts that have been made in the past towards increasing the use of fly ash, such as being part of building materials, the need remains to provide commercially acceptable wallboard that can be made with fly ash and which still has the requisite strength and density. Additionally, the wallboard with fly ash must be cost competitive including from the standpoint of developing a satisfactory process that can efficiently manufacture the wallboard.
In accordance with the present invention, wallboard is made from a composition that includes at least fly ash, water and a first binder. The wallboard has two members held on opposite sides of the composition. These two members are typically made from paper products and form the relatively rigid backing for the composition. The first binder may be subject to a foaming action in order to provide better surface interaction and adhesion between the first binder and the fly ash. In one embodiment, the first binder, in combination with at least some of the water, is caused to foam.
The wallboard can be characterized by its thickness. Traditionally, wallboard can have a one-half inch thickness and a five-eighths inch (fireproof or fire resistant) thickness. Regardless of which of these two thicknesses are employed, the amount of fly ash by weight is in the range of about 60%-66% and preferably about 63% by weight, the water is in the range of about 31%-37% and preferably about 34.5% by weight, and the first (or more than one) binder is in the range of about 1.8%-2.4% and preferably about 2.0% by weight. It should be understood that other materials could be part of the composition; however, each of the fly ash, the water and the binder remains in its respective range.
In a preferred embodiment, the first binder is part of a binder solution and there is a second binder that is part of a foam solution. In the most preferred embodiment, the first binder solution has about 5.75% polyvinyl alcohol (PVA) by weight and the foam solution has about 4.85% polyvinyl alcohol (PVA) by weight. Although it is not necessary that the second binder of the foam solution and the first binder of the first binder solution be the same, it is necessary that these two components be chemically compatible. It is also preferred that the first binder be different from polyvinyl acetate. In one embodiment, the composition includes a small amount of fiber material, such as being less than 1% by weight of the composition weight. Importantly, the composition must have a desired viscosity when the composition is initially disposed or located between the first and second members. The viscosity at that time is in the range of about 600,000 to about 1,500,000 (centipoise). Furthermore, the wallboard after being made using the composition has a strength of between about 80.0 to about 130.00 (lbs.) and a density between about 0.58 to about 0.79 (gm/ml) (36.20-49.30 lb./cu. ft.). The strength amount is based on use of an industry standard that can be identified as the xe2x80x9cnail pullxe2x80x9d test which measures the force necessary to push a standard nail through a wallboard having a specified thickness. The wallboard is also substantially homogeneous in that, for any cross-section thereof, an area of 0.1 square inch is essentially the same as any other area of 0.1 square inch.
With respect to making the composition, a first vessel or bin is utilized that contains the solid material(s), which include at least the fly ash. In one embodiment, such as wallboard with ⅝ inch thickness, the solid materials also include a fibrous material (e.g. glass fiber) in a minor amount. In preferred embodiment, a second vessel or bin houses the binder and a third vessel or bin holds the solution to be foamed, such as including a second binder which can be the same as the first binder. In this embodiment, the second binder can move or is transported from the third vessel to a foaming area such as a foaming nozzle that receives the second binder or other foamable substance (e.g., a sufficient amount of a foaming agent may be included), together with air that is introduced into the foaming nozzle. When these three vessels are utilized, their outputs are eventually received by a mixer for combining the binder solution having the first binder, the foamable solution having the second binder, together with the fly ash, as well as any other solid material that might be utilized.
The output of the mixer is input or sent to a wallboard forming subsystem that is utilized in joining the outer paper pieces or members to the composition, together with other steps or stages associated with making the wallboard.
With respect to controlling these operations, at least one control system is provided. The control system, whether it is a single system or includes a plurality of cooperating controllers, can be used to control the outputs from the vessels in connection with providing a homogenous composition having the desired viscosity output from the mixer. In that regard, the control system, in addition to including processing and regulating capabilities and functions, can include a viscosity metering device that monitors the viscosity of the composition output from the mixer. Depending on the determined, current value or magnitude of viscosity, the control system can control or regulate the inputs of solid material(s) and binders to the mixer. Such control can involve controlling the states, positions or activations of variously positioned pumps and/or valves, as well as feed mechanisms, such as an auger.
With further regard to the process for making the wallboard, after the composition is output by the mixer having the desired viscosity, it is input to the wallboard forming subsystem that can include a conveyor on which a first or lower member, preferably made of a paper material or the like, is located. A controlled portion of the composition can be continuously applied to this lower member, which portion was output by the mixer. It is preferred that the output of the mixer be adjacent to the conveyor, although such positioning is not necessary. As the composition over the first member is moved using the conveyor, it is evened or smoothed, typically applying desired pressure or a force. Then, a second or upper member is provided that overlies the composition. Subsequently, the combination of the two members and the composition therebetween can be subject to pre-heating and a further pressure applying step can be utilized. The preheating may be desirable to cause the materials to harden or set faster. However, it may be appropriate to utilize chemicals, agents or other additives that decrease the setting or hardening time and/or may provide greater strength. Preferably but not necessarily after any preheating stage, the combination of the composition and the two members are cut. The wallboard can be cut while it is on the conveyor, while the conveyor is moving or while it is stationary. The cut wallboard pieces or panels are also subject to a heating stage. After the heating stage, the wallboard is essentially a finished product.
It is noted that during the pre-heating stage, the composition includes bubbles that have been formed using at least the first binder. Maintaining a substantial number of such bubbles is important in order to achieve the desired density and strength of wallboard. Such bubbles result in stronger and more stable closed cells in the composition. To accomplish this, at least the first binder is involved with providing bubbles with a film of sufficient thickness so that they continue to hold air during the pre-heating and do not burst or otherwise fail to maintain a desired number of bubbles. During the pre-heating, at least a desired number, such as a majority, of the bubbles continue to hold air due to their sufficient thickness and the surrounding substances (e.g., hardening of the composition) so that the air cannot escape. Additionally, during the pre-heating, the composition expands to some degree over its volume before the pre-heating. This is expected and appropriate in connection with achieving desired wallboard density. However, it is important that any expansion during the subsequent heating stage be limited. That is, the expansion of the composition during the heating stage should be less than the expansion during the pre-heating.
In view of the foregoing summary, a number of salient features of the present invention are readily discerned. A wallboard composition is provided that includes substantial amounts of fly ash thereby making use of a material that is abundant and for which it is advantageous to find acceptable, productive uses thereof. The wallboard composition has critical ranges of fly ash, water and binder. These critical amounts by weight relate to providing the necessary viscosity of the composition prior to its being combined with the outer members that form the wallboard. The wallboard with the composition has a desired density and more than sufficient strength including satisfying appropriate building standards. In addition to the amounts of fly ash that must be utilized, a certain binder must be incorporated that provides a sufficient film or bubble wall thickness so that a proper wallboard density is achieved.
Additional advantages of the present invention will become readily apparent from the following discussion, particularly when taken together with the accompanying drawings.